Method for forming a pattern and a semiconductor device

ABSTRACT

The present invention relates generally to a method for forming a pattern, and in particular, to a method for forming a pattern for the formation of quantum dots or wires with 1~50 nm dimension using the atomic array of a single or poly crystalline material. The electron beam lithography method preferably uses the phase contrast atomic image of a single or poly crystalline material itself.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a method for forming apattern and a semiconductor device, and in particular, to a method forforming a pattern for the formation of quantum dots or wires with 1˜50nm dimension using the atomic array of a crystalline material and to themanufacture of functional devices that have such a structure.

The present invention relates generally to a method for forming apattern and a semiconductor device, and in particular, to a method forforming a pattern for the formation of quantum dots or wires having anano or tens of nano meter order using the atomic array of a single or apoly crystalline material and to the manufacture of functional devicesthat have such a structure. The electron beam lithography method inaccordance with the present invention uses the phase contrast atomicimage of a single or a poly crystalline material itself.

2. Description of the Related Art

The formation process of quantum dots or wires becomes the core processfor the fabrication of an electronic, magnetic, or optical device withquantum dots or wires as the application of such devices is increasinglyexpected. A fundamental operating principle of such devices is based onquantum mechanical results that the physical properties of the particleare greatly affected by its size as it becomes nanometer-sized.Particularly, there are many researches for the single electrontransistor which has been suggested as the alternative to MOS device inorder to overcome the limitation of the MOS device that has beendeveloped continuously for 40 years.

Previous researches on the formation processes of quantum dots or wirescan largely be divided as follows.

First, there is a method in which one or a few quantum dots or wires areformed by AFM (Atomic Force Microscopy), STM (Scanning TunnelingMicroscopy) and electron beam lithography. This method has thecapability to form the quantum dots or wires whose size and location arecontrolled experimentally, but has difficulty in applying to massproduction because of a low throughput.

Second, there is a method in which quantum dots or wires are formed bythe process of patterning and etching. In this method, patterning meansthe formation process of quantum dots or wires on the substrate by theelectron beam direct-writing, or by the etching of the chemicalsubstance which was imprinted by the mask or mold made with an electronbeam.

Third, there is a method in which quantum dots or wires are formed bythe nucleation at the early state of phase transition of materials. Thismethod has can be applied to mass production, but has problems incontrolling the size, density or distribution of quantum dots or wires.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide a methodfor forming a pattern using a crystal structure of a single or a polycrystalline material as a mask.

It is another object of the present invention to provide a method forforming quantum dots and wires of uniform size and density which can becontrolled by patterning a layer using a crystal structure of a singleor a poly crystalline material as a mask.

It is a further object of the present invention to provide a method forforming quantum dots and wires using a crystal structure of a single ora poly crystalline material for fabricating semiconductor devices inpractice.

It is still another object of the present invention to provide asemiconductor device having the structure of quantum dots or wires. Theforegoing and other objects of the present invention can be achieved byproviding a method for forming a pattern wing a crystal structure of asingle or poly crystalline material as a mask. According to one aspectof the present invention, a method for forming a pattern using a crystalstructure of a single or poly crystalline material is comprising thesteps of locating the material having a crystal structure in the chamberof the transmission electron microscope; radiating an electron beam tothe material; forming a pattern from a lattice image of the materialhaving a crystal structure on the surface of an irradiated material suchas a electron beam resist deposited substrate by diffracted electronbeam and transmitted electron beam passed through the material.

Preferably, the lattice image is formed by a method of the phasecontrast imaging.

Preferably, the material having a crystal structure is processed into athickness of a few tens of nanometer.

Preferably, the irradiated material is an electron beam resist depositedmaterial on a semiconductor substrate.

Preferably, the semiconductor substrate has been applied with anelectron beam resist deposited on after deposition of a gate oxide andan amorphous silicon on the substrate in which source and drain regionsare already formed.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIGS. 1A to 1C illustrate lattice points moved one-dimensional,two-dimensional, three-dimensional respectively.

FIG. 2 illustrates an arrangement of atoms around the lattice point.

FIG. 3 illustrates the 7 crystal systems and the 14 Bravais lattices.

FIG. 4A illustrates a unit cell of crystal structure of Al.

FIGS. 4B to 4D illustrate two-dimensional projection patterns of Alcrystal through the [100], [110], [111] crystallographic orientations.

FIG. 5A illustrates a unit cell of crystal structure of Si.

FIGS. 5B to 5D illustrate two-dimensional projection patterns of Sicrystal through the [100], [110], [111] crystallographic orientations.

FIG. 5E illustrates a three-dimensional projection pattern when FIG. 5Cis rotated 56° clockwise and 15° azimuthally.

FIG. 6A illustrates a unit cell of crystal structure of GaAs.

FIGS. 6B to 6D illustrate two-dimensional projection patterns of GaAscrystal through the [100], [110], [111] crystallographic orientations.

FIG. 6E illustrates a three-dimensional projection pattern when FIG. 6Cis rotated 56° clockwise and 15° azimuthally.

FIG. 7 is a schematic view of a first embodiment of TransmissionElectron Microscopy(TEM) according to the present invention.

FIG. 8 is a schematic view of a second embodiment of TEM according tothe present invention.

FIG. 9 is a schematic view of a third embodiment of TEM according to thepresent invention.

FIGS. 10A to 10F are sectional views sequentially illustrating anembodiment of a process of fabricating single electron transistor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings. In thefollowing description, well-known functions or constructions are notdescribed in detail.

At first, to help understanding of the invention, crystal structures ofgeneral materials and their various schematic figures will beillustrated.

It is well known that the materials in the earth are composed of atomsand molecules which contain a few atoms and particularly, solid materialis classified into a crystalline material in which the atoms aresituated in a repeating or periodic array over large atomic distancesand an amorphous material that lacks a systematic and regulararrangement of atoms over relatively large atomic distances. Theresearch on the periodic array of the atoms started in 1912 by Max vonLaue who found x-ray diffraction. In 1913 W. H. Bragg and his son solvedthe crystal structure of diamond and salt by x-rays and in 1920 Ewaldintroduced the concept of the reciprocal lattice. Until now, the crystalstructures of more than a hundred thousand of organic or inorganiccompounds in the earth have discovered.

If a point is moved by the distance a parallel to a certain direction,it matches second point and if that is moved the same way, that becomesthird point. As the same way one point is moved parallel repeatedly, anarray of points is made as shown FIG. 1A. This array of points which isgenerated with being repeatedly shifted at regular distance along thegiven direction is called lattice. The motion of shifting a point inthis manner is called translation and expressed as vector a. Hereregular distance, that is, the magnitude of the vector |a|=a is calledperiod or unit period. In this array of points, each point is the sameand if one point is marked as an origin.

That is, r=ma where m is an integer from −∞ to ∞,

Point network plane is generated by translation this array of points tothe other direction as shown FIG. 1B and this is called lattice plane.When this lattice plane is translated to translation c, the thirddirection which is not parallel to this plane, three dimensional pointnetwork plane is generated and called space lattice. In this spacelattice, each lattice point is described by position vector r from theorigin and expressed as, r=ma+nb+pc

where, m, n, p are integers between −∞ to ∞. The space lattice isinfinitely spread in infinite space as shown FIG. 1C.

It is said that a crystal is macroscopically uniform, because theproperties of a part of crystal are the same as those of the other partat arbitrary distance away. FIG. 2 shows an imaginary crystal structure.A certain point p in this crystal is described by the position vector,L, and the unit translation vectors of this lattice a, b, c,$\begin{matrix}{L = {{X\quad a} + {Y\quad b} + {Z\quad c}}} \\{= {{( {m + x} )a} + {( {n + y} )b} + {( {p + z} )c}}} \\{= {( {{m\quad a} + {n\quad b} + {p\quad c}} ) + ( {{x\quad a} + {y\quad b} + {z\quad c}} )}} \\{= {r + {r\quad l}}}\end{matrix}$

where, X, Y, Z are real numbers and x, y, z are decimals between 0and 1. That is, a certain point in space is expressed by rl whichrepresents a crystal lattice, and r which represents position vector inthe lattice. Here, the unit lattice described by three translationvectors is called a unit cell.

When a certain point in the crystal is fixed as the origin (0,0,0), alllattice points generated from this point (0,0,0) are identical with theorigin and have the same properties. That is to say, whatever point isfixed as the origin in the crystal, every lattice point made bytranslation from this point is identical. Identical means all properties(including the geometric form of the surroundings around this point,chemical properties such as a kind of neighbor atoms, or physicalproperties such as electron density, potential difference) are exactlythe same.

All crystalline includes one of the 7 crystal systems by the relationbetween three vectors, a, b, c that determine unit cell. TABLE 1 showsthe relation between lattice parameters which defines three axes of unitcell.

TABLE 1 Crystal structure Crystal system Lattice parameter Cubic Cubic A= b = c α = β = γ = 90° Hexagonal Hexagonal A = b ≠ c α = β = 90° γ =120° Trigonal Rhombohedral A = b = c α = β = γ ≠ 90° TetragonalTetragonal A = b ≠ c α = β = γ = 90° Orthorhombic Orthorhombic A = b = cα = β = γ = 90° ≠ Monoclinic Monoclinic 1. c-unique a ≠ b ≠ c α = β =90° ≠ γ Monoclinic Monoclinic 2. b-unique a ≠ b ≠ c α = γ = 90° ≠ βTriclinic Triclinic A ≠ b ≠ c α ≠ β ≠ γ ≠ 90°

Also all crystalline have one of the 14 Bravais lattices as shown inFIG. 3. It is classified according to the number of lattice points inunit cell as the primitive cell (P) has one lattice point in unit cell,the base-centered cell (A, B or C) has one lattice point in the centerof one plane, the face-centered cell (F) has lattice points in thecenter of each plane and the body-centered cell (I) has one latticepoint in the center of the unit cell.

The crystal structure, of which more than a hundred thousand of organicor inorganic materials have been known until now, is classified as the 7crystal systems and the 14 Bravais lattices. Actual crystal structure iscomposed by the arrangement of one or more of the same or differentatoms in each lattice point which is included in the 14 Bravais lattice.

Next, some examples of such a crystal structure are given and thepattern from the arrangement of atoms which is shown when those crystalstructures are projected to the given crystallographic orientation isexplained.

For example, Al is a cubic crystal system (a=b=c) and the face-centeredcell of the Bravais lattices, so it has four lattice points in one unitcell. The crystal structure of Al is made when one Al atom lies in onelattice point, and the lattice constant of Al is a=b=c=0.404 nm.Therefore the structure of Al unit cell is shown as FIG. 4A. FIGS. 4B,4C, and 4D show the projection pattern of atomic arrangement through[100], [110] and [111] crystallographic orientations.

The other example is Si of a diamond crystal structure. Si is cubiccrystal system and the face-centered of the Bravais lattices like Al(Face Centered Cubic). So it has four lattice points in one unit cell,but it has two atoms in one lattice point unlike simple face-centeredcubic crystal system (lattice parameter a=b=c=0.543 nm). Therefore thereare eight atoms in a Si unit cell. FIG. 5A shows the unit cell of Si. Asthe same way FIGS. 5B, 5C and 5D show the two-dimensional projectionpattern of atomic arrangement through [100], [110] and [111]crystallographic orientations. FIG. 5E shows the pattern when FIG. 5B isrotated 56° clockwise and 15° azimuthally. As shown FIG. 5C, the imagelooks like several lines. This is the evidence that depending onprocessing techniques, Si single crystal can apply to the form ofquantum wires in a single electron transistor device.

And another example is the crystal structure of GaAs. GaAs has a crystalstructure of cubic like Al and Si, and the face-centered Bravais latticelike Si. But, unlike Al of a simple cubic lattice and Si of a diamondcrystal structure, GaAs has a crystal structure which is an one Ga atomand one As atom at one lattice point.(lattice parameter a=b=c=0.565 nm)FIG. 6A shows the unit cell of crystal structure of GaAs. By the sameway, FIGS. 6B, 6C, 6D are two-dimensional projection patterns of GaAscrystal through the [100], [110], [111] crystallographic orientations.FIG. 6E shows the pattern when FIG. 6C is rotated 56° clockwise and 15°azimuthally in the same manner of FIG. 5E. Like Si, the single crystalof GaAs is a good example applicable to the quantum wire formation.

Al, Si, and GaAs mentioned above are only a few examples among thealready known crystal structures over a hundred thousand. Thus, thesedemonstrations indicate that very various patterns generated byelectrons transmitted in the two dimensional plane can be obtained. Ofcourse, this generated pattern is dependent on the crystallographicorientation as well as on the crystal structure.

The atom's array of the crystal can be observed using the phase-contrastmethod in high resolution TEM (transmission electron microscopy). As theelectron microscopy has developed, it is possible to distinguish theatoms alignments with the range of 0.14 nm-0.20 nm under 200 kV-300 kVof an accelerating voltage.

In the phase contrast method, atomic images can be made by the phasedifference between diffracted electron beam and transmitted electronbeam which is generated from the crystal material. This method has amuch better resolution than other methods such as a diffraction contrastor an absorption contrast.

FIG. 7 shows how an interference image is made by the phase difference.As shown in FIG. 7, the image is formed by the phase difference betweendiffracted electron beams and transmitted beams in the plane ofprojection.

The material (5) with the thickness of a few tens of nanometer is puttedin a chamber. Electron beam(3) can transmit this kind of thickmaterial(5). At the same time, the interaction between the material(5)and the transmitted electrons cause the electron beam separated todiffracted beams and transmitted beams.

Transmitted beam and diffracted beam, which were separated during thetransmission through the material (5), pass an objective lens (7) and anaperture (8). As a result of the interference with these two beams, thelattice image of crystal structure is formed. In the present invention,the image plane means the plane where transmitted beam and diffractedbeam make the lattice image of a crystal structure by their interferenceduring the transmission of material (5). This image formed in the imageplane (9) can be magnified, used as it is or contracted by the lens. Inthe present invention, the pattern is formed using this image.

The distance of the interference fringe is proportional to the spacingof lattice, which is the distance between atoms. As a result, the atomicarray can be distinguished by this interference pattern.

In fact, in the practical high resolution TEM, the first interferenceimage which is formed by the objective lens is magnified sequentially byother lens which is located behind the objective lens. As a result, thisimage which is magnified by several hundreds of thousand can be observeddirectly. In general, magnification of an objective lens is the rangefrom several decades to several hundreds. For example, when themagnification of an objective lens is one hundred, 3 nm spacing ofatomic array is magnified into 30 nm that is a spacing of interferenceimage. When this interference image is magnified or down scaled again byother lens, the image of atomic line and atoms with the range from a fewnm to a few tens of nm will be obtained.

The present invention is intended to make to pattern by using thecrystal structure of a single or a poly crystalline sample material. Theelectron beam is radiated to the sample material which has a crystalstructure and is loaded in the chamber. When the electron is transmittedthrough this sample, the lattice image is formed by the phase contrastmethod. The phase contrast is generated by the interference between thetransmitted electron beam and the diffracted electron beam. By usingthis lattice image of the crystal structure, the pattern for thefabrication of the functional device can be obtained.

In this embodiment, method for forming a pattern using a crystalstructure of a single or a poly crystalline material is to fabricate thesemiconductor devices, by placing of a single or a poly crystallinematerial having a crystal structure in the chamber of the TEM,irradiating electron beam, ten, forming a lattice image of that materialby a method of the phase contrast imaging, and finally fanning thepattern in the semiconductor substrate from a lattice image of thematerial having a crystal structure.

In the present invention, the method to fabricate the pattern is asfollows. The lattice image which is formed in the image plane ismagnified or down-scaled to the intended size. Then, this image canexpose the electron beam resist which is applied on the semiconductormaterials. This image can be formed by using some parts of the latticeimage of the sample material loaded in the chamber.

In the high resolution TEM that is used currently, the resolution of theatomic scale is already guaranteed. Therefore, in a method for forming apattern introduced in the invention, if lattice images of a crystalstructure that is formed at the imaging plane is scaled down instead ofscaling up, then semiconductor substrate that is applied with the photoresist is exposed to this image. As a result, it is possible to formpatterns of a few angstrom on the semiconductor wafer.

The shape of the pattern, which is formed by using a crystal structureof a material by a method of the invention, is determined by a crystalstructure of the material used. Therefore, the location of atoms anddistances of the atoms in a crystal structure of a material is embodiedin the final semiconductor device as it is shaped.

FIG. 8 shows another example of the present invention.

As shown in FIG. 8, a single or a poly crystalline material that isprocessed into the sample with a thickness of a few tens of nanometer(13) is placed at the center of to chamber in order to be passed throughby the electron beam (11). The electron beam (11) is split intodiffracted beam and transmitted beam by the interaction with thematerial (13) which have a crystal structure.

Transmitted beam and diffracted beam, into which the incident beam issplit during the transmission through the material (13), pass anobjective lens (15) and an aperture (17). As a result of theinterference with these two beams, the lattice image of crystal

structure is formed. In the present invention, the image plane means theplane where transmitted beam and diffracted beam make the lattice imageof crystal structure by their interference during the transmission ofmaterial (13). The intermediate lens (19) magnifies the image, which isformed at the image plane.

In the present invention, spacing of the atomic plane of a material,alignment of the electron beam, the degree of vacuum in the column ofthe TEM, the degree of correction of a astigmatism, and the brightnessof the electron gun determine the accelerating voltage. Generally, thecurrent accelerating voltage is the range from 100 keV to 1 MeV. If thespacing of the atomic plane is about 3 angstrom, the acceleratingvoltage of the 100 kV is used, and if the spacing of the atomic plane isabout 2 angstrom, the accelerating voltage of the 200 kV is required.

The single electron transistor device, which is fabricated by a methodof the invention, has the structure that is constituted by asemiconductor substrate, a source region that is formed in thesemiconductor substrate, a drain region spaced from the drain region inthe semiconductor substrate, and a layer that includes quantum dots.These quantum dots are placed on the semiconductor region locatedbetween the drain region and the source region and have the same patternwith the lattice image of the material in the chamber

FIG. 9 shows another example of the present invention.

As shown in FIG. 9 a single or a poly crystalline sample material (23)of a few tens of nanometer is placed at the center of the chamber inorder to be passed through by the electron beam (21). The electron beam(21) is split into diffracted beam and transmitted beam by theinteraction with the material (23) which has a crystal structure.

Transmitted beam and diffracted beam, into which the incident beam issplit during the transmission through the material (23), pass anobjective lens (25) and an aperture (27). As a result of theinterference with these two beams, the lattice image of crystalstructure is formed. In the present invention, the image plane means theplane where transmitted beam and diffracted beam make the lattice imageof crystal structure by their interference during the transmission ofthe material (23). The intermediate lens (29) can reduce the image,which is formed at the image plane.

FIGS. 10A to 10F are sectional views sequentially illustrating anembodiment of a process of fabricating a single electron transistor.

FIG. 10A illustrates the steps of forming a source (31) and a drainregion (33) in Si wafer.

FIG. 10B illustrates the steps of growing a gate oxide film(35) of a fewnm thickness on the Si wafer and depositing the amorphous Si(37) of afew nm thickness on the gate oxide(35).

FIG. 10C illustrates the steps of coating electron beam-resist(39) onthe amorphous Si(37).

Then place a silicon having [110] zone axis in the TEM chamber to formthe pattern as shown in FIG. 5E.

FIG. 10D illustrates the steps of radiating the electron beam to exposethe electron beam-resist film(39).

FIG. 10E illustrates the steps of removing the electron beam-resistfilm(39), and etching the amorphous silicon(37) using the plasma processto form quantum dots.

FIG. 10F illustrates the steps of depositing control oxide(41) andpoly-silicon(43) on the amorphous silicon(37) on that region formedquantum dots and then patterning. As a result, the single electrontransistor device is fabricated.

In the fabricated device, the pattern of quantum dot that is made on thegate oxide(35) is the same with the pattern of Si, which has [110] zoneaxis. The size of quantum dot is 5 nm, and the density is about 10 exp12/cm².

In accordance with the present invention as described above, the quantumdots can be formed and controlled using the lattice image of a single ora poly crystalline crystal structure.

While the present invention has been described in detail with referenceto the specific embodiments, they are mere exemplary applications. Thus,it is to be clearly understood that many variations can be made byanyone skilled in the art within the scope and spirit of the presentinvention.

What is claimed is:
 1. A method for forming a pattern using a crystalstructure of a single or a poly crystalline material, comprising thesteps of: locating said material having a crystal structure in achamber; radiating an electron beam to said material in said chamber;forming a pattern from a lattice image of said material formed as aresult of interference between diffracted beam and transmitted beampassed through said material on the surface of an irradiated material.2. The method of claim 1, wherein said material having a crystalstructure has a thickness of a few tens of nanometer.
 3. The method ofclaim 1, wherein said lattice image of material is formed by a method ofthe phase contrast imaging.
 4. The method of claim 1, wherein saidirradiated material is a semiconductor substrate.
 5. The method of claim1, wherein said irradiated material is an electron beam resist depositedon a substrate.
 6. A method for forming a quantum dot using a crystalstructure of a material as a mask, comprising the steps of: locatingsaid material having a crystal structure in a chamber; radiating anelectron beam to said material in said chamber; forming a pattern from alattice image of said material formed as a result of interferencebetween diffracted beam and transmitted beam passed through saidmaterial on the surface of an electron beam resist material on asubstrate, patterning said electron beam resist material on saidsubstrate.
 7. The method of claim 6, wherein said lattice image ofmaterial is formed by a method of the phase contrast imaging.
 8. Anelectron beam lithography method for forming a pattern using a crystalstructure of a single or a poly crystalline material, comprising thesteps of: providing a film of electron beam resist on a substrate;irradiating an electron beam to said material in a chamber; forming apattern from a lattice image of said material formed as a result ofinterference between a diffracted beam and a transmitted beam passedthrough said material on said film of electron beam resist on asubstrate.
 9. The method of claim 8, wherein said material having acrystal structure has a thickness of a few tens of nanometer.
 10. Themethod of claim 8, wherein said lattice image of material is formed by amethod of the phase contrast imaging.
 11. The method of claim 8, furthercomprising passing said diffracted beam and said diffracted beam througha aperture prior to said step of forming said pattern.
 12. An electronbeam lithography method for forming a pattern using a crystal structureof a single or a poly crystalline material, comprising the steps of:providing a film of electron beam resist on a substrate; irradiating anelectron beam to said material in a chamber; forming a pattern from alattice image of said material formed as a result of interferencebetween a diffracted beam and a transmitted beam passed through saidmaterial on said film of electron beam resist on the substrate,patterning said film of electron beam resist on the substrate.
 13. Themethod of claim 12, wherein said lattice image of material is formed bya method of the phase contrast imaging.
 14. The method of claim 12,wherein said material having a crystal structure has a thickness of afew tens of nanometer.
 15. The method of claim 12, further comprisingpassing said transmitted beam and said diffracted beam through anaperture prior to said step of forming said pattern.